Allow breaking subtree for element-iterator

[Tidyzq]

1. Added type for ElementIterator, which is mostly the same as shadow-decendants-root-first or composed-decendants-root-first but skips iterate on the subtree when callback returns false instead of breaking the whole iteration.
   • shadow-decendants-subtree
   • composed-decendants-subtree
2. Fix iteration breaking on shadow-decendants-root-first and shadow-decendants-root-last